Underwater transducer



June 18, 1963 B. B. GAULD 3,094,536

UNDERWATER TRANSDUCER Filed June 15, 1956 I2 I //f I3 INVENTOR.

B. B. GA ULD ATTORNEY United States Patent "ice This invention relates to underwater transducers utilizing electromechanically-responsive ceramic elements for converting electric oscillations into sound waves, and vice versa.

An object of the invention is to provide a simple, eifieient, reliable and inexpensive transducer of this type.

A more specific object is to provide an effective transducer having a single electromechanically-sensitive vibratile element of relatively small cross-sectional area and a sound-radiating and absorbing face of substantially larger area.

Other more specific objects and features of the invention will appear from the description to follow.

It is old to use transducers having a single longitudinal-vibratile ceramic element, one end of which constitutes the working face in acoustic coupling relation with the water. However, the coupling efficiency and directional characteristics of a transducer vary with the area of the working face, and it is often impractical to employ ceramic elements of large enough end area to provide the desired directional characteristics. The usual solution has been to use an array of small elements. One such transducer is disclosed and claimed in Camp et a1. Patent No. 2,797,399, issued June 25, 1957, assigned to The Bendix Corporation, which transducer contains an array of seven small solid cylindrical ceramic elements. Such an array has the advantages over a single large solid ceramic cylinder of being much cheaper, because of difficulties in manufacturing large ceramic elements.

The transducer of the present invention utilizes a single ceramic element and has substantially the same electrical and acoustical characteristics as the seven-element transducer of the prior application. This is accomplished by employing a composite integral vibrator element consisting of a longitudinally vibratile ceramic ring having a rigid disk bonded to its front end and a heavy ring bonded to its rear end. The disk constitutes the working face and is made as rigid as possible to vibrate as a piston; to this end, it is preferably relatively thick and of some relatively light, strong material, such as aluminum. The rear ring is to provide mass at the rear end of the vibrator element and is preferably made of lead or other dense material. It is substanatially coextensive laterally with the ceramic ring, so that it is not subject to bending stresses, and its thickness is determined by the mass required and not by stiffness requirements.

A full understanding of the invention may be had from the following detailed description, with reference to the drawing, in which:

FIG. 1 is a front view of a transducer in accordance with the invention.

FIG. 2 is a sectional view taken along the line II-II of FIG. 1.

Referring to the drawing, the transducer therein disclosed comprises a body 11 molded or otherwise formed from rubber or similar material defining a closed recess 11a in which a vibrator 10 is positioned. Two mounting holes 1112 are provided near the middle of the body for screwing or bolting it against the under surface of a boat with the rear surface 110 lying against the boat and the front surface 11d facing downwardly.

It will be observed from FIG. 1 that the recess 11a is located adjacent one end of the body, and the latter 3,094,635 Patented June 18, 1963 is extended therefrom in wedge form to a leading edge 112 which is pointed toward the forward end of the boat so that it divides the water and reduces turbulence at the active face 11d. A cable 12 containing the electrical conductors is preferably extended from the rear end of the body (the end opposite the leading edge 112). The cable extends through an aperture in a neck portion 11 of the body which is compressed tightly about the cable by a clamp 13.

The front end of the recess 11a is closed by a rubber sound window 14, the outer surface of which is flush with the front surface 11d of the remainder of the body.

The vibrator 10 is a composite element comprising an electromechanicallyresponsive ring 10a, a front aluminum disk 10b, and a rear lead ring 100, all firmly bonded together at their contact faces. The ceramic and lead rings 10a and 10c have cylindrical inner and outer faces, and flat end faces. The outside diameter disk 10b is at least as great as that of the ceramic ring 10a, and is preferably slightly larger, as shown in the drawing. To facilitate axial alignment of the ceramic and lead rings in assembly (as by use of a mandril), their inside diameters may be exactly the same. Likewise, to facilitate axial alignment of the disk 10b with the rings, the outside diameter of the disk and lead ring may be the same.

The vibratory force of the ceramic ring is preferably applied to the disk 1012 at an annular zone of the latter spaced radially inwardly from the outer cylindrical face thereof, to increase the area of the disk that can be used with a given size of ceramic ring without increasing the bending stresses in the disk. In this connection, it will be understood that a large disk diameter is desirable to improve the efficiency of transfer of acoustic energy between it and the water, and to improve the directional characteristics. The use of a disk of larger diameter than the outside diameter of the ceramic ring has the further advantage that it permits a smaller and cheaper ceramic ring to be used, and also reduces the bending stresses in the disk and its tendency to vibrate in secondary modes.

The ceramic ring has the usual silver electrodes 10d and 10e on its front and rear annular faces, respectively, to which are connected the conductors in the cable 12. The electrodes may be formed by painting the front and rear surfaces of the ceramic element with silver paint and baking them to leave a thin film of metallic silver.

The longitudinal or axial dimension of the vibrator assembly is less than the depth of the recess 11a, and the vibrator is supported with the front face of the disk 1% in contact with the sound window 14 by a disk 15 of acoustic insulating material such as cellular neoprene. This disk 15 fills the space between the rear wall of the recess 11a and the lead ring so that the vibrator 10 is supported within the body by the disk 15 and the diaphragm 14. The front face of the disk 10b is firmly bonded to the sound window 14, so that the latter prevents any lateral shifting of the vibrator within the recess 11a.

It is usually desirable to provide in the cable 12 a central conductor 12a and a concentric conductor 12b surrounding the conductor 12a. The conductor 12a is connected to the rear electrode 102 of the ceramic element 10a, and the outer conductor 12b is connected to the front electrode 10d. The concentric conductor 12b is preferably at ground potential, and to shield the electrode 10c from extraneous electric fields a metallic shield disk 16 is provided between the disk 15 and the rear wall of the recess 11a and is connected to the conductor 12b of the cable.

The ceramic element 10a may be of any well known material, such as barium titanate, and is prepolarized in accordance with well-known practice so that it responds to mechanical vibrations applied thereto through the sound window 14 to generate potential between its electrodes d and 102, and responds to alternating electrical potentials applied to said electrodes to expand and contract longitudinally and thereby cause the entire element 10 to vibrate longitudinally by contraction and expansion, with resultant vibratory movement of the front face of the disk 10b. The entire vibrating device is preferably of length equal to one-half the wave length of sound therein at the operating frequency. At a frequency in the neighborhood of 100,000 cycles per second, the ceramic element 10a may be .245 inch thick; the aluminum disk 1 10b may be .301 inch thick; and the lead ring 100 may be .125 inch thick.

The particular advantages of the may be summarized as follows:

(a) The use of the hollow ceramic cylinder enables a reduction of the capacity without diminishing the effective area of the vibrating face in acoustic coupling relation with the water.

(b) The hollow rear mass, in the form of the lead ring 100, has the advantage of providing a desirable mass at the rear end of the vibrator that may be constructed of relatively weak material (with respect to bending).

(c) The combination of the ceramic ring with the front disk of larger diameter provides an active element employing a relatively small amount of material with a working face of relatively large area.

Although for the purpose of explaining the invention a particular embodiment thereof has been shown and described, obvious modifications will occur to a person skilled in the art, and I do not desire to be limited to the exact detail-s shown and described.

"I claim:

1. In an underwater transducer: a watertight casing defining a cavity and having juxtaposed flat front and rear walls, said front wall constituting a sound window; a layer of acoustic insulating material positioned against said rear wall; a unitary longitudinally-vibratile vibrator positioned in said cavity and extending between and supported by said layer of insulating material and said front wall, respectively, the front end of the vibrator being bonded to said front wall for acoustic connection therewith and present construction lateral support thereby; said vibrator comprising a longitudinally vibratile, electromechanically-responsive element and front and rear mass element-s bonded thereto,

. said front element being of lesser density and larger di- 6. "A transducer according to claim 5 in which said mass elements have the same external diameter and the electromechanically-responsive element has a lesser external diameter.

7. An electromechanical transducer system comprising electromechanical transducer means sandwiched between two pieces of solid materials which have relatively dissimilar densities and constituting with said pieces a mechanical vibrator, said system being dimensioned to vibrate as a half-wave vibrator in the direction of a line through said pieces and said transducer means.

References Cited in the file of this patent UNITED STATES PATENTS 2,508,544 Shaper May 23, 1950 2,520,938 Klein Sept. 5, 1950 2,638,577 Harris May 12, 1953 2,753,543 Rymes July 3, 1956 2,797,399 Camp June 25, 1957 FOREIGN PATENTS 527,250 Belgium Mar. 31, 1954 OTHER REFERENCES Sonics, Hueter-Bolt, pub. by John Wiley and Sons, Inc., New York, copyright 1955, pages 97-99.

Mil-C-17831A (Ships), February 16, 1956, Military Specification Communication Set, Sonar, Swimmers Underwater Telephone, 21 pp., Fig. 3 relied on (page 21). 

7. AN ELECTROMECHANICAL TRANSDUCER SYSTEM COMPRISING ELECTROMECHANICAL TRANSDUCER MEANS SANDWICHED BETWEEN TWO PIECES OF SOLID MATERIALS WHICH HAVE RELATIVELY DISSIMILAR DENSITIES AND CONSTITUTING WITH SAID PIECES A MECHANICAL VIBRATOR, SAID SYSTEM BEING DIMENSIONED TO VIBRATE AS A HALF-WAVE VIBRATOR IN THE DIRECTION OF A LINE THROUGH SAID PIECES AND SAID TRANSDUCER MEANS. 